1. Field of the Invention
The invention relates to a pitch measurement device for measuring a pitch that indicates the frequency at which a body part such as the leg moves while walking or running, to an electronic instrument equipped with a pitch measurement function, and to a pitch measurement method; and more particularly to a technology for determining pitch from the body movement signals detected during running or walking.
2. Description of the Related Art
Pitch counters are known that use a means such as an acceleration sensor that can detect the movements of a body (body movements) to obtain body movement signals and that determine a pitch from these body movement signals. Conventional pitch counters, for example, use a method that first amplifies body movement signals, next converts them into pulses, and then counts the pulses obtained. As shown in FIG. 16(a), the pulse wave obtained using this method has irregular pulse intervals depending on the running state, resulting in large measurement errors even if the pulses are counted by setting a specific threshold value. Therefore, a method has been adopted that improves the detection precision by counting pulses in units of two using a mask signal that can set a specific non-sensitive time during pulse counting, as shown in FIG. 16(a). The pitch indicating the frequency at which the right and left legs or hands move while running is normally between 150 to 200 times/minute, which can be converted into pulse cycles of between 0.3 to 0.4 seconds. Therefore, by using a mask signal with a masking time, or non-sensitive time, of 0.5 seconds, the pulse signals resulting from the conversion of body movement signals can be counted in units of two and pulses can be counted as pulses having pulse cycles of between 0.6 and 0.8 seconds. Therefore, pitches can be measured at high precision.
However, such a method results in extremely large errors if the walking pitch is measured using a mask signal in which the masking time was set for measuring running pitch. That is, as shown in FIG. 16(b), the pitch during walking is between 100 and 150 times. Therefore, a signal with a cycle of between 0.4 and 0.6 seconds is obtained when the body movement signal is converted into pulses. If a mask signal having the same masking time of 0.5 seconds as that used during running is applied to the above signal, pulses will be counted in units of one when the pitch is 100 times/minute, resulting in an error. Therefore, to use a conventional pitch counter to measure running or walking pitch, it is necessary to externally switch the mask signal between running and walking before starting pitch measurement. Pitches cannot be measured accurately if this switching operation is not performed before the start of the measurement, and may sometimes result in totally meaningless data. Furthermore, in an electronic instrument equipped with other multiple functions in addition to the pitch-measurement function, the user must memorize the method of switching mask signals, making the instrument extremely inconvenient to use.
Additionally, when body movement signals are supplied to the aforementioned measurement method using mask signals, it is not possible to use a personal computer, etc. to analyze their pitch unless it is known beforehand whether the data was obtained during walking or running.